Process and mixture for hardening steel



Patented July 23, 1935 UNITED STATES PATENT OFFICE Richard Watson Cross, Chicago, Ill.

No Drawing. Application September 20, 1932, Serial No. 634,077

12 Claims.

This invention relates to a novel and improved process for hardening steel and a chemicallyinert mixture for use therein and consists of the matters hereinafter described and more particularly pointed out in the appended claims.

In the ordinary commercial process of hardening steel, as heretofore carried on, the surface exposed to the heat-of the flame in the hardening process is oxidized and various component elements of the steel are volatilized and driven off, leaving a scale. As a result, the metal is left after quenching with a rough uneven surface which requires grinding or polishing, or in the case of edge tools, requires sharpening.

The object of my invention is to provide a novel process for hardening steel whereby these objectionable features of the earlier processes are eliminated and the surface of the steel and, in the case of tools, the edges of the tools, are left, after the hardening process, with-the original surface and edge given the steel body at the beginning, rendering unnecessary any after dressing, grinding or sharpening. Thus with this process the steel body may be ground to its intended, finished surface or edge, which will be unchanged by the process.

The enormous advantage, saving and economy of a process eliminating said objectionable features of the'earlier process will be manifest to those familiar with the art.

In the hardening of steel it is necessary to heat the steel brgy to high temperatures, varying from 1500 Fahrenheit to 2500 Fahrenheit, depending upon the steel and the purpose to which the steel is to be put and the hardness required of the steel to meet the conditions it is subjected to when in use. After the steel has been raised to such temperature in the ordinary process, it must immediately be removed from the flame or crucible and submerged in a quenching medium, since otherwise the continued action of the high heat would tend to burn the steel.

In carrying out my process, however, instead of subjecting the steel body, the tool, or the like, to a direct action of flame or heat, I insert the steel body into a fused mixture of mineral elements and fluxes, chemically inert as to each other and as to the constituents of the steel body at the temperatures required by the process,

which mixture has been raised to that predetermined temperature required to bring the metal, when quenched, to the required hardness. The steel body may be allowed to remain in said fused mixture which is maintained at the said prede- 5 termined temperature, for an indefinite period longer than the period of time required tobring it to said predetermined temperature, without harm, and in fact, with beneficial result, as will be later pointed out.

The mixture as described herein, consists largely of silica, feldspar and borax, which are chemically inert as to each other and as to the constituents of the steel body at the temperature of fusion required in carrying on the process. While silica and feldspar each acts as a fiux for the other, the mixture requires a flux, as borax, andat higher temperatures an additional flux or fluxes and/or stifi'eners, so that it will fuse at the predetermined hardening temperature to a sticky, plastic, or syrupy consistency. Due to said plastic or syrupy, sticky character of the fused mixture at the hardening temperature, the mixture will adhere to the steel body 25 upon its withdrawal from the mixture, thus pro.- viding a protective coating for the steel body to protect it from oxidation or other chemical change during and after its removal from the mixture and during the quenching process. The 30 coating of the mixture is designed to crystallize and crumble when cooled in the quenching procesS and at the higher temperatures additional ingredients are included in the mixture to promote this crystallization and crumbling, so that the bond between the steel and the mixture will be broken after the steel body is quenched.

I present below examples of formulae for the mixture for several hardening temperatures with 40 the percentages given by weight:-

In the range of 1500 to l900 Fahrenheit:

Silica 31.4 Feldspar 38.3 45 Borax 14.0 Sodium bicarbonate 14.0 English ball clay 2.3

In the range of 1900 to 2250 Fahrenheit:

Silica 22.0 Feldspar 27.3 Borax 12.2

Bicarbonate of soda 10.1 Whiting 10.1 Magnesium carbonate 4.3 English ball clay 2.0 Florida kaolin or English china. clay 1.0 Steatite .4 Zinc oxide 10.2 Tin oxide .4

In the range of 2250 to 2500 Fahrenheit:

Silica l 30.7 Feldspar 20.4 Borax 6.1 Bicarbonate of soda 5.1 Whiting 14.3 Magnesiumj carbonate 2.1 English ball clay 6.1 Florida kaolin or English China clay 4.1 Zinc oxide 10.3 Tin oxide .8

The above named ingredients are ground dry and are thoroughly mixed together. They are then melted in a crucible and brought to the temperature required for hardening the steel to be treated. The process of heating brings the mixture to a sticky plastic or syrupy consistency.

The silica and feldspar react upon each other as fluxes to lower the fusing temperature of the mixture of the two. The silica and feldspar, fused alone or together, would become liquid shortly above their respective softening temperatures, which are above the hardening temperatures designed to be attained- An additional flux or fluxes are thus required. The clay or clays at the higher hardening temperatures stiffen the mixture and give it the required plastic consistency over a wider temperature range. However, the clay or clays, when used, if added-alone to the mixture, would too greatly raise the fusing temperature of the silica and feldspar. The borax and/or the sodium carbonate, also the whiting and magnesium carbonate in the mixtures for the higher temperatures, act as fluxes to counteract the tendency of the clay to raise the fusing temperature and act to reduce the temperature of fusing to the required hardening temperature.

The word flux as used herein and in the claims, means a solid substance of low fusion which, when blended with a more refractory solid substance, as for example feldspar and/0r silica, will cause a lowering of the melting point of the latter substance or, in other words, will increase the ease of fusion of the other substance. In determining upon the flux to be used, care must be had that it is of such chemical structure that when fused to the temperature required, it will not give off chemical or acid gases which will etch or pit the steel or will combine with the steel so as to give a case or surface hardening to the steel body. The above named elements, borax, sodium carbonate, whiting and magnesium carbonate are well known fluxes of the kind.

The clays used, namely, English ball clay, Florida kaolin and/or English china clay, are free of impurities and for this reason are adapted for use in the mixture.

The zinc and tin oxides used at the higher hardening temperatures, not required for like result at the lower hardening temperatures, produce in the mixture a tendency to crystallize or crumble at lower temperature, so that the bond between the steel and the coating or film of the mixture adhering to the steel body when it is withdrawn from the mixture, will be broken upon cooling by quenching.

The several formulae above given represent the best proportions for the higher hardening temperature named in each case, but may likewise be used to advantage down to the lower hardening temperature given. However, as a chemist will understand, these proportions may be varied for intermediate lower specific hardening temperatures to get a better result than the general formulae given.

The composition of the mixture is such that even when heated it does not attack the surface of the article which is being treated nor does it attack thecontainer. In other words, it is chemically inert at all temperatures within the maximum practicable heating range and does not change its chemical composition with continued use. In consequence, it does not deposit a sludge in the bottom of the container to interfere with the absorption of heat nor does it fume or give off poisonous or irritating gases.

To harden a steel body, as for example, a high speed steel tool, a quantity of the chemical mixture is placed in a suitable crucible and is heated ture remains plastic or syrupy, thereby facilitating the insertion and withdrawal of pieces to be heated. Such quantity of the mixture is used that, when placed in the crucible and fused, there is sufficient to submerge the part of the steel body or tool which it is designed to harden.

After the mixture has been raised to the predetermined, required temperature (in the case of the high speed steel tool-2300 Fahrenheit) the steel body is immersed in the plastic mixture.

The sticky mixture closely adheres to the piece inserted and thus prevents all volatilization of the essential ingredients in the metal so that the chemical composition of the piece remains unchanged.

Upon first insertion of the steel into the mixture, that part of the mixture in contact with and adjacent to the steel body, immediately tends to cool down to approximately the temperature of the cool steel. This part of the mixture thereafter protects the surface of the steel from a sudden change of temperature, the two-the steel body and the mixture in the immediate vicinity of the steel body-being gradually heated up together by the heat of the surrounding mixture. The temperature of the body of the mixture is gradually imparted to the tool, the temperature of which is finally raised to that of the mixture. In the above respect, my mixture differs from liquid heating mediums which transmit heat rapidly to the insorted piece, thereby causing strains, My mixture has a high heat capacity but at the same time a low conductivity which permits the heat to be absorbed gradually and uniformly.

The steel body is allowed to remain in the plastic mixture, which is maintained at the predetermined temperature, until it is heated throughout to that temperature, the length of time depending upon the diameter or size of the steel body which is to be hardened, a smaller body of course requiring less time than a larger body, or a tool of smaller diameter requiring less time than a tool of larger diameter. The length of time in each case may be predetermined by experiment and test for the size of the piece and for the particular character of steel contained in the tool or other steel body to be hardened.

The minimum length of time required being approximately determined, the tool maybe allowed to remain in the mixture at the predetermined temperature for an indefinite longer period of time, thus insuring the proper seating of the molecular grains or particles throughout the tool without any danger of harming or deteriorating the metal, as its surface is at all times covered and protected by the plastic mixture in which it is submerged.

After the tool has remained at the predetermined temperature for the required length of time, it is withdrawn from the plastic mixture. When withdrawn, the part of its surface which has been submerged will be found to be covered completely and uniformly with a film, coating or skin of the mixture which still protects the surface. It is immediately submerged with this film or coating upon it in either oil or water or some other quenching medium, which cools it and thus completes the hardening process. By the use of the mixture, the tool may be raised to the exact, desired temperature, since it is possible readily to determine the temperature of the mixture and to maintain it at that temperature.

The skin or film adhering to the surface continues to protect said surface from the sudden shock onfirst insertion in the quenching mediumand from any disintegrating effect of the cooling medium during the cooling process, particularly when water is used as the cooling medium. It not only cushions the chilling effect upon first immersion in the quenching medium, but it slows down the cooling during the lower temperature zones in which occurs most of the cracking and warping. Skin effect is eliminated and the hardening takes place uniformly through the piece. The film or coating remains intact until the tool or other steel body has been reduced to a certain low temperature, when the tool becomes black (about 800 Fahrenheit), when the plastic skin or film begins to crack and crumble and finally falls off, leaving the hardened surface of the tool or steel body exposed with its original surface and/or edge.

The protection given by the film to the tool during the quenching operation protects the steel also from any deleterious gases which might be absorbed at high heat from the quenching medium. That portion of the mixture carried over on the piece from the heating bath to the quenching bath can be reclaimed and used over again in view of the fact that it has not suffered any change in composition through the heating and chilling process. Q

In the use of my improved process for hardening steel, it is possible to secure a uniform heat throughout the entire steel body or steel tool without danger of burning or otherwise detericrating the surface of the tool. Oxidation, contraction and burning of the steel is eliminated.

The steel body or tool may be held at the hardening temperature for an indefinite period of time, at least as long as an hour, without any loss of carbon or of the toughening or hardeningconstituents such as cobalt, nickel, chromium, manganese, tungsten, vanadium, molybdenum or other components constituents, which would be volatilized and driven 01f by the required high temperature in the ordinary way of hardening steel, these being retained in the steel body. With the improved process it is possible to apply heat of a uniform temperature at just that part of the steel body which it is required to harden. Steel tools hardened by my process are tougher, more elastic and not nearly so brittle as when hardened by the ordinary-process.

These and many other advantages are inherent in the new process by reason of the fact that the steel body in the hardening process is not subjected to the direct action, either of the heat or of the cooling medium, but is at all times protected by the plastic mixture in which it is submerged during the heating process and by the film or coating of said mixture which covers it.

The improved process may be applied to annealed metals and may be used for recovering (that is to say, hardening) tools that have been hardened and have lost their temper in use.

I claim as my invention:-'-

1. A mixture for use in hardening steel when fused at a hardening temperature ranging from 1500 to 1900 Fahrenheit, consisting of the following ingredients substantially in proportions by weight named: silica 31.4%; feldspar 38.3%; borax 14.0%; sodium bicarbonate 14.0%; and English ball clay 2.3%.

2. A mixture for use in hardening steel when fused at a hardening temperature ranging from 1900 to 2250 Fahrenheit, consisting of the following ingredients substantially in proportions by weight named: silica 22.0%; feldspar 27.3%; borax 12.2% bicarbonate of soda 10.1%; whiting 10.1%; magnesium carbonate 4.3%; English ball clay 2.0%; Florida kaolin 1.0%; steatite .4%; zinc oxide 10.2%; and tin oxide .4%.

3. A mixture for use in hardening steel when fused at a hardening temperature ranging from 2250 to 2500? Fahrenheit, consisting of the following ingredients substantially in proportions by weight named: silica 30.7%; feldspar 20.4%; borax 6.1%; bicarbonate of soda 5.1%; whiting 14.3%; magnesium carbonate 2.1%; English ball clay 6.1% Florida kaolin 4.1% ;'zinc oxide 10.3%; and tin oxide .8%. Y

4. A mixture for use in hardening steel when fused at a hardening temperature ranging from 1500 to 2500" F. which contains silica 22-31.4%, feldspar 20.4-38.3%, borax 61-14%, sodium bicarbonate 5.1-14%, and English ball clay 2-'6.1%.

5. The process of hardening steel, which consists in submerging a body of steel to be treated in a chemically inert fused mixture raised to the predetermined hardening temperature, said mixture containing silica, feldspar, borax, sodium bicarbonate and clay substantially free of impurities, in retaining said steel body in said fused mixture, while maintaining said mixture at said hardening temperature, until the part to be treated has been brought throughout to the temperature of said'fused mixture, in then withdrawing of the steelvaluable chemical said steel body with a film of the mixture adhering to the treated part of said steel body, and in then quenching said steel body.

6. The process of hardening steel, which consists in submerging a body of steel to be treated in a chemically inert fused mixture raised to the predetermined hardening temperature, said mixture containing silica, feldspar, borax, sodium bicarbonate and clay substantially free of impurities proportioned to fuse to a plastic or syrupy, sticky consistency at the said hardening temperature, in retaining said steel body in said fused mixture, while maintaining said mixture at said hardening temperature, until the part to be treated has been brought throughout to the temperature of said fused mixture, in then withdrawing said steel body With a film of the mixture adhering to the treated part of said steel body, and in then quenching said steel body.

'7. A mixture for use in hardening steel, said mixture being chemically inert and containing silica, feldspar, borax, sodium bicarbonate and clay substantially free of impurities.

8. A mixture for use in hardening steel, said mixture being chemically inert and containing silica, feldspar, borax, sodium bicarbonate and clay substantially free of impurities proportioned to fuse to a plastic or syrupy, sticky consistency at the hardening temperature for which it is designed for use.

9. The process of hardening steel, which consists in submerging a body of steel to be treated in a fused mixture raised to the predetermined hardening temperature, said mixture containing silica, feldspar and borax proportioned so that when fused it will be chemically neutral or basic throughout the range of the hardening temperature, in retaining said steel body in said fused mixture, while maintaining said mixture at said hardening temperature, until the part to be treated has been brought throughout to the temperature of said fused mixture, in then withdrawing said steel body with a film of the mixture adhering to the treated part of said steel body, and in then quenching said steel body.

10. The process of hardening steel, which consists in submerging a body of steel to be treated in a fused mixture raised to the predetermined hardening temperature, said mixture containing silica, feldspar, borax and sodium bicarbonate proportioned so that when fused it will be chemically inert or basic throughout the range of the hardening temperature, in retaining said steel body in said fused mixture, while maintaining said mixture at said hardening temperature, until the part to be treated has been brought throughout to the temperature of said fused mixture, in then withdrawing said steel body with a film of the mixture adhering to the treated part of said 

